Well, that’s what they’re doing some places. The batteries assets are not in private homes usually though, they’re by themself or run by power-consuming industries. Batteries are expensive though, and they degrade quickly if you use them wrong. In the EU, ENTSO-E defines the market rules, trade systems and messaging systems that energy companies and asset owners play by. Sometimes the revenue-generating asset is a battery, sometimes it’s a hot water boiler, wind park, factory, hydro plant etc.